Showing papers by "Tomasz Jakubczyk published in 2017"

Coherent coupling of individual quantum dots measured with phase-referenced two-dimensional spectroscopy: Photon echo versus double quantum coherence

Abstract: We employ two-dimensional (2D) coherent, nonlinear spectroscopy to investigate couplings within individual InAs quantum dots (QD) and QD molecules. Swapping pulse ordering in a two-beam sequence permits to distinguish between rephasing and non-rephasing four-wave mixing (FWM) configurations. We emphasize the non-rephasing case, allowing to monitor two-photon coherence dynamics. Respective Fourier transform yields a double quantum 2D FWM map, which is corroborated with its single quantum counterpart, originating from the rephasing sequence. We introduce referencing of the FWM phase with the one carried by the driving pulses, overcoming the necessity of its active-stabilization, as required in 2D spectroscopy. Combining single and double quantum 2D FWM, provides a pertinent tool in detecting and ascertaining coherent coupling mechanisms between individual quantum systems, as exemplified experimentally.

Exploring coherence of individual excitons in InAs quantum dots embedded in natural photonic defects: Influence of the excitation intensity

Abstract: We acknowledge the financial support by the European Research Council (ERC) Starting Grant PICSEN (grant no 306387)

Antireflective Photonic Structure for Coherent Nonlinear Spectroscopy of Single Magnetic Quantum Dots

Abstract: This work presents epitaxial growth and optical spectroscopy of CdTe quantum dots (QDs) in (Cd,Zn,Mg)Te barriers placed on top of the (Cd,Zn,Mg)Te distributed Bragg reflector. The photonic mode formed in our half-cavity structure permits enhancement of the local excitation intensity and extraction efficiency of the QD emission, while suppressing the reflectance within the spectral range covering the QD transitions. This allows us to perform coherent, nonlinear, resonant spectroscopy of individual QDs. The coherence dynamics of a charged exciton is measured via four-wave mixing, with the estimated dephasing time T2 = (210 ± 40) ps. The same structure contains QDs doped with single Mn2+ ions, as detected in photoluminescence spectra. Our work therefore paves the way toward investigating and controlling coherence of individual excitons coupled, via s,p-d exchange interaction, with individual spins of magnetic dopants.

Impact of environment on dynamics of exciton complexes in a WS$_2$ monolayer

Abstract: Scientific curiosity to uncover original optical properties and functionalities of atomically thin semiconductors, stemming from unusual Coulomb interactions in the two-dimensional geometry and multi-valley band structure, drives the research on monolayers of transition metal dichalcogenides (TMDs). While recent works ascertained the exotic energetic schemes of exciton complexes in TMDs, we here employ four-wave mixing microscopy to indicate that their subpicosecond dynamics is determined by the surrounding disorder. Focusing on a monolayer WS$_2$, we observe that exciton coherence is lost primarily due to interaction with phonons and relaxation processes towards optically dark excitonic states. Notably, when temperature is low and disorder weak excitons large coherence volume results in huge oscillator strength, allowing to reach the regime of radiatively limited dephasing and we observe long valley coherence. We thus elucidate the crucial role of exciton environment in the TMDs on its dynamics and show that revealed mechanisms are ubiquitous within that family.

Determination of radial quantum dot position in trumpet nanowires from far field measurements

Abstract: A quantum dot embedded in a trumpet nanowire has been shown to be a good candidate for realising an efficient on-demand single-photon source [1, 2]. At the lateral quantum dot position the diameter of the nanowire only supports two guided modes — the HE11 and TE01 modes. These modes are excited by the quantum dot after recombination of an electron-hole pair. The slow expansion of the nanowire diameter secures an adiabatic propagation of the modes through the taper meaning that the occupation of the HE11 and TE01 modes will remain the same at the top of the trumpet nanowire (see Fig. 1 right). It is for now not possible to control the radial position of the quantum dot in the nanowires and thus it is important to experimentally determine this after fabrication.

Optical localization of quantum dots in tapered nanowires

Abstract: In this work we have measured the far-field emission patterns of In As quantum dots embedded in a GaAs tapered nanowire and used an open-geometry Fourier modal method for determining the radial position of the quantum dots by computing the far-field emission pattern for different quantum dot locations.

Determination of radial quantum dot position in trumpet nanowires from far field measurements

Abstract: A quantum dot embedded in a trumpet nanowire has been shown to be a good candidate for realising an efficient on-demand single-photon source [1, 2]. At the lateral quantum dot position the diameter of the nanowire only supports two guided modes — the HE11 and TE01 modes. These modes are excited by the quantum dot after recombination of an electron-hole pair. The slow expansion of the nanowire diameter secures an adiabatic propagation of the modes through the taper meaning that the occupation of the HE11 and TE01 modes will remain the same at the top of the trumpet nanowire (see Fig. 1 right). It is for now not possible to control the radial position of the quantum dot in the nanowires and thus it is important to experimentally determine this after fabrication.